ANDREW DOYLE / SINGAPORE
Investigators have discovered possible evidence of fatigue cracking in the rear fuselage of the China Airlines (CAL) Boeing 747-200 which mysteriously broke up at high altitude on 25 May with the loss of 225 lives.
The find is significant because it is the first potential evidence of a pre-existing structural abnormality in the 22-year-old aircraft. As a result of the discovery, investigators are focusing on section 46 of the rear fuselage, between passenger doors three and five.
In a possibly related development, it has also emerged that the aircraft suffered structural damage during a tailscrape incident on landing in February 1980 and was repaired. The work included the installation of a 3m (10ft)-long metal doubler, and the possible fatigue cracks were found in the same area as the repair site.
"We have found some wreckage pieces that potentially show signs of metal fatigue," says lead investigator and Taiwan Aviation Safety Council (ASC) managing director Kay Yong.
"The main focus of the investigation is the aft-fuselage section," he adds.
The ASC has sent the first batch of specimens to Taiwan's Chung-shan Institute of Technology (CSI) for analysis. The suspected fatigue cracks were noticed because they look different to the "tear" fractures typically induced by high stresses as an aircraft breaks up.
Based on spectrum analysis of the cockpit voice recorder, Yong says it is "more likely" the 747 suffered a rapid, rather than explosive, decompression.
The revelation that the CAL 747 suffered a tailscrape and was repaired suggests the report into a 1985 crash involving a Japan Airlines Boeing 747-100SR could be of relevance. This aircraft's bulkhead failed after it was inadequately repaired following an earlier tailscrape.
Investigators have recovered 60% of the CAL wreckage, including all four engines and most of the relatively intact rear pressure bulkhead.
Source: Flight International
